Modeling of Ocean Mesoscale Variability and Coupled Ocean-Atmosphere Interaction in the Northwest Tropical Atlantic Ocean.

Abstract:

The Northwest Tropical Atlantic is characterized by the strong North Brazilian Current (NBC), its rings, and numerous mesoscale eddies ceaselessly interacting with the persistent trade winds and trade cumuli. Near the coast, the ocean stratification is maintained by the Amazon and Orinoco river discharges which, in turn, influence the vertical mixing and the circulation in the region. Breaking waves and swells are ubiquitous under the trade winds, and hence, the wave-induced mixing and wave-mediated air-sea fluxes are expected to modulate the eddy variability and air-sea interaction. Our study aims to enhance understanding of the air-sea fluxes mediated by the ocean eddies and waves and evaluate their impacts on the ocean and atmosphere.

An orderly set of ocean and wave model simulations are being conducted to examine the effects of the river, tides, and wave-ocean interactions for the period of ATOMIC/EUREC4A field experiments. The river discharges, as expected, significantly influence the upper-ocean stratification near the river mouths, where salinity is reduced (by 10psu), mixed layer depth shoaled (by 40m), and ocean current accelerated (>1 m/s). Far downstream responses in the circulation emerge within a few months, most notably in the propagation and intensity of the mesoscale eddies, contributing to large anomalies in temperature, salinity, and currents. Coastal vertical mixing and SST are significantly impacted by the tides, as is the lateral dispersion of the river plumes, impacting broader-scale upper-ocean stratification. Wave model simulations demonstrate that the key inputs to the wave-based flux formulation, such as the direction, period, and steepness, are notably altered near the density fronts associated with NBC, its rings, and mesoscale eddies. The results from the ocean and wave modeling efforts guide our ongoing fully coupled ocean-atmosphere (and wave) model simulations to quantify their impacts on the atmosphere, including low-level clouds.